The present invention relates to a method of securing elastic band between two layers of material which are made at least partially of meltable material. The invention also relates to an elastic band secured between two layers of material and intended for use in articles intended for one-time use only, such as disposable diapers, sanitary napkins, surgical dressings, protective clothing or the like, and also to a diaper which includes such an elastic band.
In the manufacture of articles intended for one-time use only, such as disposable diapers or the like, it is desirable that these articles can be worn comfortably, will function effectively and fit properly, besides having an attractive appearance. These attributes are often compared with the attributes of corresponding multi-use articles. Such articles are traditionally manufactured from very soft, woven or knitted textile materials which are comfortable to wear and in which great care has been taken in cutting and sewing the materials from which the articles are made.
When manufacturing disposable articles, however, it is not possible to use expensive materials or to apply complicated and expensive manufacturing methods, since the articles would then demand an unreasonably high price. Instead, the traditional textile materials are usually replaced with plastic film, different types of non-woven fabric and tissue layers. Techniques such as gluing and welding are used, instead of sewing the articles together.
One particular problem in this respect is that of providing elastication edges, for instance elasticated leg, waist and sleeve bands. Normally, elastication in the form of elastic tape, bands or treads is secured along the edges of the article to be elasticated with the aid of melt adhesive. This method has several drawbacks, however. For instance, the glue has an uncontrollable stiffening effect on the elastic devices used, therewith impairing the elasticity of said devices. In the case of disposable diapers, for instance, the elastic devices, or elastication, is normally placed between two casing layers, normally a plastic film and a non-woven fabric layer. The elastic devices are mounted between the casing layers and fastened thereto while in a stretched state, whereafter the elastic devices return to their non-stretched, shorter state and gather together those parts of the casing layers to which the devices are attached. As a result, there is formed, primarily in the plastic film relatively sharp folds which are liable to chafe the skin of the wearer. Gluing of the elastic devices also causes the elasticated edge to become hard and chafing. These known elasticated edges are thus not as comfortable as would be desired.
Another drawback is that the formation of folds in the outer layers, or casing layers, results in the formation of channels between the elastic devices and the wearer""s skin. This is particularly disadvantagous when the elastic devices are placed around the leg and waist parts of diapers, since these channels provide routes through which excreted body fluids can escape from the diaper. Neither can the known elastications be considered to satisfy the desire for an attractive, fabric-like appearance, but instead result in a wrinkled and shapeless finished article.
Difficulties are also experienced in the manufacture of articles where the elastication is glued thereto. The main problem is that the glue, which may be a melt glue or a thermosetting glue for instance, requires a certain amount of time for heating and cooling or drying the glue after it has been applied. During this time period, it is necessary to maintain the elastication in a stretched state, which presents a problem in a continuous manufacturing process. Furthermore, the necessity of handling a glue requires the provision of expensive special-duty equipment for avoiding troublesome occurrences, such as the adhesion of glue to machine rolls and knives.
Hitherto, it has not been found possible to provide in a simple and ready fashion elasticated edges which possess varying degrees of elasticity within different parts of the edges, or where certain parts of said edges are completely inelastic, various methods of providing elastication in limited areas, or with varying degrees of pretensioning, in a continuous manufacturing process have been proposed, for instance, in GB 2 113 983, EP 184 072, U.S. Pat. Nos. 4,642,151, 4,425,173, 4,486,192, 4,081,301, 4,711,683 and 4,642,109.
The present invention, however, now provides a simple method of securing an elastic band between two material layers comprised of at least partly meltable material while avoiding the drawbacks experienced with earlier known elastication.
The inventive method is may characterized m that perforations in the form of holes and/or slots are formed in the elastic band, in that the elastic band is placed between the two material layers; and in that material layers opposite said perforations are bonded together by heat fusion through said perforations.
The invention also relates to an elastic band secured between two material layers.
When such an elastic band is fastened onto an article which is intended for one-time use only, there is obtained a soft, non-chafing elastic edge. This is mainly due to the fact that no glue is used to fasten the elastication, but that the elastication is held mechanically between two mutually bonded material layers. Consequently, both the elastication and the material layers will retain their original softness and suppleness. This is also due to the fact that the elastic band can move to a certain extent in relation to the material layers surrounding said band, thereby enabling said layers to pleat or fold independently of one another when the elastic band relaxes. Distinct from the earlier known elastications, which gather the surrounding material layers into sharp, chafing folds, the material layers will form around an inventive elastic band soft, rounded folds which bulge outwardly from the elastication. This is because the material layers are bonded to the elastic band by mutually spaced bonds, those pats of the material layers located between the bonds are not bonded at all.
It should be mentioned that in the present context, the expression elastic band refers to an elongated elastic body whose width has a much-greater extension than the perforations formed therein in accordance with the invention.
A further advantage provided by an inventive elastic band resides in the possibility of achieving varying degrees of stretchability or elasticity within different regions of one and the same elastic band, simply by changing the bonding pattern. This feature is particularly useful in the case of all-in-one type diapers, for instance. Diapers of this kind comprise an absorbent pad which is enclosed between a liquid permeable, inner casing layer and a liquid-impermeable, outer casing layer or backing sheet. The elastication is normally applied along the edges of the absorbent pad, so as to form elasticated waist and leg edges. The diapers also include self-adhesive fastener tabs, which are attached to the corners of the diaper on the backed sheet, i.e. on that part of the diaper which is distal from the wearer in use. The tabs function to hold together the sides of the diaper, so as to obtain a trouser-like configuration around the abdomen of the wearer.
The fastener tabs are secured over the front part of the diaper, i.e. that part of the diaper which faces towards the wearer in use.
When securing the faster tabs, it is desirable that the surface of the diaper material are as smooth as possible. This applies particularly to that part of the front part of the diaper on which the fastener tabs are intended to be secured in use. If this part of the diaper is wrinkled and irregular, the fastener tabs will not grip securely and there is a risk that the diaper will not be held together during use. An advantage is also afforded when the tab rents on the rear part of the diaper have inelastic, smooth regions, since this facilitates securing of the tabs to the diaper during manufacture, and also provides more positive attachment of the fastener tabs. If the tape-fastening areas are elastic and the fastener tabs are secured to the diaper with the elastic devices in a stretched state, there is a serious risk that the tabs will loosen from the diaper when the elastic devices are relaxed from their stretched state and subsequently contract. The present invention, however, enables totally inelastic regions to be readily provided, by selecting an elastic-device bonding pattern such that the elastic devices are broken, down in these regions and loose their elasticity.
It is also possible to adjust the degree of elasticity around the leg openings of the diaper, for instance. The greatest elasticity is preferably found within those regions in which the elasic devices are attached to the crotch region of the diaper, i.e. that part of the diaper which, in use, is intended to lie between the wearer""s thighs. On the other hand, there is preferably chosen in those parts of the elastic devices which extend along the front and rear portion of the diaper a bonding pattern which will reduce the elasticity of the elastic devices.
A further advantage afforded by an elastic band configured in accordance with the invention is that it imparts an aesthetically attractive, well-tailored appearance to the finished article. The elastic band appears soft and comfortable, whereby the finished article looks to be extremely comfortable, to the naked eye.
When an inventive elastic band is secured to the surrounding material layers at solely mutually spaced bonding locations, which permits the material layers to fold or pleat freely in relation to the elastic device, there is obtained an airy elastic edge and the soft material folds give a certain padding effect. The risk of the skin becoming irritated is very small, since the folds in the material layers bonded to the elastic band provide a certain ventilating effect, which will keep the skin beneath the elastic band substantially dry during use. The elastic band may also be made from an open-cell foam material, so as to provide air ventilation through the actual band itself, provided that at least one of the surrounding material layers is permeable to air.
A number of advantages are also obtained when manufacturing an elastic band in accordance with the invention. For instance, the troublesome handling of glue is avoided, as is also the need of drying or heating and cooling melt adhesive. Furthermore, there is avoided the need of complicated devices for varied stretching of the elastic devices, or of devices for handling pieces clipped from said elastic devices.